1. Field of the Invention
The present invention relates to a color projector adopting three display devices, and more particularly, to a color projector in which the size or position of display devices with respect to each color is changed so that chromatism can be compensated for.
2. Description of the Related Art
In a typical color projector, an image formed by a display device such as an LCD panel is projected onto a screen by using an additional light source. The color projector is divided into a transmission type and a reflection type according to the type of display device.
FIG. 1 is a view showing the optical arrangement of a conventional transmission type color projector. Referring to the drawing, the conventional transmission type color projector includes a light source 10, first and second dichromatic mirrors DM1 and DM2 for splitting the light ray emitted from the light source 10 into red (R), blue (B) and green (G) colors, a plurality of total reflection mirrors M1, M2 and M3 for allowing the light rays split by the first and second dichromatic mirrors DM1 and DM2 to proceed along three different paths, first through third LCD panels 21, 23 and 25, arranged on the proceeding path of each of the split light rays, a color prism 30 for synthesizing images according to the respective colors formed by the first through third LCD panels 21, 23 and 25, and a projection lens unit 40 for projecting the synthesized color image formed while passing through the color prism 30 toward a screen 50 by magnifying the same.
Each of the first through third LCD panels 21, 23 and 25 is formed of a plurality of pixels arranged on a plane. Each pixel independently driven polarization-modulates an incident light according to input video signals and also makes light rays of a polarization component proceed toward the color prism 30. The first LCD panel 21 forms an image of an input red (R) light which is reflected by the first dichromatic mirror DM1 and passes through the second dichromatic mirror DM2; the second LCD panel 23 forms an image of an input green (G) light which is reflected by the first and second dichromatic mirrors DM1 and DM2; and the third LCD panel 25 forms an image of an input blue (B) light passing through the first dichromatic mirror DM1.
The color prism 30 has first through third incident surfaces 31, 33 and 35 disposed to face the first through third LCD panels 21, 23 and 25, respectively, and a single exhaust surface 37 facing the projection lens unit 40. The color prism 30 also has a first mirror surface 30a for reflecting the light input through the first incident surface 31 and passing the light input through the second and third incident surfaces 33 and 35, and a second mirror surface 30b for reflecting the light input though the third incident surface 35 and passing the light input through the first and second incident surfaces 31 and 33. The projection lens unit 40 projects the image, which is formed by the first through third LCD panels 21, 23 and 25, synthesized by passing through the color prism 30 and output through the exhaust surface 37, toward the screen 50 by magnifying the same.
In the conventional transmission type projector having the above structure, the first through third LCD panels 21, 23 and 25 have the same specifications. That is, the sides of the first through third LCD panels 21, 23 and 25 facing one another have the same length h. Also, the first through third LCD panels 21, 23 and 25 each are arranged to be separated the same distance from the projection lens unit 40. When the optical distances from the respective first through third incident surfaces 31, 33 and 35 of the color prism 30 to an incident surface 41a of a first lens 41 forming the projection lens unit 40 are the same, the first through third LCD panels 21, 23 and 25 are installed to be separated the same distance d from the first through third incident surfaces 31, 33 and 35, respectively.
A typical lens exhibits chromatism which is an aberration depending on the wavelength of an input light. Referring to FIG. 2, the light input parallel to a convex lens 60 is theoretically focused at a focal point f. Actually, of the input light, a red (R) light which has a relatively long wavelength focuses at a focal point FR which is a position farther than the focal point f of the convex lens 60, while a blue (B) light which has a relatively short wavelength focuses at a focal point FB which is a position closer than the focal point f of the convex lens 60.
Thus, due to the chromatism, the color images with respect to red, green and blue colors formed by the first through third LCD panels 21, 23 and 25 of FIG. 1 focus on the screen 50 at different sizes. Also, as the difference in magnification is generated with respect to red, green and blue colors, a degree of mismatch of the red, green and blue color images increases at the periphery of the screen 50, thereby deteriorating the quality of image. Therefore, as the projection lens unit 40 necessarily has an additional optical structure to compensate for the above chromatism, the structure of the projector becomes complicated.
Further, the projection lens unit 40 should be designed considering distortion and field curvature of an image formed on the screen 50. Here, the projection lens unit 40 is not able to perfectly correct both distortion and chromatism. Thus, when the projection lens unit 40 is mainly adjusted to correct the distortion that is easily noticeable to a viewer, an additional lens to correct chromatism is needed. In this case, however, it is a drawback that only a limited correction of chromatism is possible.
To solve the above problems, it is an objective of the present invention to provide a color projector which can compensate for chromatism by changing the size and/or position of a display device with respect to each color to improve image quality and also a compact design of the projection lens unit is possible.
Accordingly, to achieve the above objective, there is provided a color projector comprising a light source, a splitting device for splitting the light emitted from the light source to proceed along first through third optical paths according to the wavelength thereof, first through third display devices, arranged on the first through third optical paths, for forming an image from an input light of a predetermined wavelength, a synthesizing means for synthesizing lights of different colors to proceed along one path by selectively transmitting or reflecting input lights passing through the first through third display devices according to the wavelength thereof, and a projection lens unit for magnifying and projecting a color image synthesized by the synthesizing device toward a screen, in which two or more display devices selected from the first through third display devices have the different sizes of effective areas where an image is formed such that chromatism generated while lights of different colors synthesized by the synthesizing device pass the projection lens unit can be corrected.
Also, to achieve the above objective, there is provided a color projector comprising a light source, a splitting device for splitting the light emitted from the light source to proceed along first through third optical paths according to the wavelength thereof, first through third display devices, arranged on the first through third optical paths, for forming an image from an input light of a predetermined wavelength, a synthesizing means for synthesizing lights of different colors to proceed along one path by selectively transmitting or reflecting input lights passing through the first through third display devices according to the wavelength thereof, and a projection lens unit for magnifying and projecting a color image synthesized by the synthesizing device toward a screen, in which the distances between two or more display devices selected from the first through third display devices and the projection lens unit are different from one another such that chromatism generated while lights of different colors synthesized by the synthesizing device pass the projection lens unit can be corrected.